Analogues of somatostatin, a tetrdecaeptide, will be synthesized primarily by solid-phase techniques and tested for inhibition of release of growth hormone, insulin, glucagon, and gastric acid secretion. On the basis of this work, conclusions will be drawn as to the relationships between the structure of the molecule and its numerous biological activities. This should make possible the development of compounds with greater clinical value due to higher specificity of action. Particularly useful would be peptides that would primarily inhibit GH release (treatment of acromegaly and angiopathies associated with diabetes mellitus), glucagon release (treatment of several forms of diabetes mellitus), gastrin and gastric acid secretion (treatment of gastric ulcers). In this respect, the design of longer-acting analogues with greater physiological stability would be of some importance. Since somatostatin is a crucial participant in the control mechanisms of numerous endocrine and exocrine systems, competitive inhibitors of the peptide might have remarkable effects on promoting release of certain hormones and attempts will be made to discover such compounds.